Lesson #1: Any time you sell a car, you should file a Release of Liability with DMV, which informs them you sold the car. It is available on the DMV website. That way, if somebody gets a ticket or, worse still, injures someone with your former car, they'll go after the new owner, not you.
If you ignore it, there may be a warrant for your arrest and the fines will go way up. I'm not really clear, but it sounds like the speeding ticket came from AZ. If you get pulled over in CA on an AZ traffic ticket, you aren't going to be extradited, but you could be arrested if you get stopped in AZ.
Arizona might also suspend your license. Since AZ and CA are members of the Interstate Compact on drivers licenses, California might recognize the suspension.
In a California traffic matter, you can do a trial by filing your declaration under penalty of perjury, which would include the fact you sold the car. You could also attach any supporting documents.
Arizona may have a similar statute. Contact the clerk of the court that sent you the ticket and ask.